Coating for the mitigation of metal whiskers

ABSTRACT

A coating for mitigating metal whiskers on a metal surface includes a polymeric coating material; and a metal ion complexing agent impregnated within the polymeric coating material, the metal ion complexing agent having a standard reduction potential (E°) that is greater than a metal in the metal surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims benefit of U.S. patentapplication Ser. No. 15/175,303, filed Jun. 7, 2016, the entire contentsof which are incorporated herein in their entirety.

BACKGROUND

The present disclosure relates to metal-containing surfaces, and moreparticularly, to methods to mitigate formation of tin whiskers ontin-containing surfaces.

Pure tin (Sn) plating has replaced tin-lead alloy solders in manyelectrical applications, for example, electrical hardware, circuit boardtraces, component leads, and ground planes. Replacing tin-lead alloysolders with pure tin plating is driven, in part, by environmental andhealth concerns about lead.

The “whisker” or “tin whisker” phenomenon is a failure mode associatedwith some electronic devices that use a number of low melting pointelements (e.g., tin (Sn), cadmium (Cd), zinc (Zn), nickel (Ni), andindium (In)) in operations such as soldering. As shown in FIG. 1, tinwhiskers 101 may be formed from a pure (or substantially pure) tin-basedsurface 100. Whiskers may also form on other surfaces, such as nickelsurfaces. Generally, metal whiskers have a small mass (for example, lessthan 100 micrograms) with a high surface area-to-volume ratio. Becausemetal whiskers are conductive and can carry high current, they mayresult in electronic shorting failures.

SUMMARY

According to one embodiment, a coating for mitigating metal whiskers ona metal surface includes a polymeric coating material; and a metal ioncomplexing agent impregnated within the polymeric coating material, themetal ion complexing agent having a standard reduction potential (E°)that is greater than a metal in the metal surface.

According to another embodiment, a coating for mitigating tin whiskerson a tin surface includes a polymeric coating material including silvernanoparticles and a complex of a tin ion and a Schiff base-containingcompound; wherein the coating is disposed on a tin surface comprisingabout 97 to about 100 atomic % (at. %) tin.

Yet, according to another embodiment, a method for mitigating tinwhiskers includes providing a substrate having a tin surface includingabout 97 to about 100 atomic % (at. %) tin; forming a polymeric coatingincluding a complexing agent that can chelate tin; and disposing thepolymeric coating on the tin surface, the complexing agent reacting withtin in a tin whisker to form a tin ion:complexing agent complex.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts:

FIG. 1 is an scanning electron micrograph (SEM) of tin whiskers formedon a tin surface;

FIG. 2A is a cross-sectional side view of a metal layer arranged on asubstrate; and

FIG. 2B is a cross-sectional side view of a coating arranged on themetal layer of FIG. 2A according to embodiments.

DETAILED DESCRIPTION

Various approaches are used to reduce or eliminate formation of metalwhiskers (e.g., tin whiskers) in electronic devices that include metalsurfaces (e.g., tin surfaces or nickel surfaces). On tin surfaces, oneapproach includes contaminating tin with another metal to prevent tinwhisker formation. However, such contamination generally usesenvironmentally unfriendly metals. Another approach to mitigating tinwhiskers includes applying a conformal coating to tin surfaces. However,tin whiskers can still grow through conformal coatings.

Accordingly, as described herein, various embodiments provide aconformal coating with an additive that complexes, or in someembodiments, chelates, metal ions in metal whiskers (e.g., tin whiskers)as they grow or extend from a metal surface. The metal in the whiskersis consumed to substantially eliminates/mitigate the whiskers. Inembodiments, the additive is a metal oxidizer that is incorporated intothe coating and reacts with the metal in the surface to consume oreliminate the tin whisker. In one exemplary embodiment, the additive isan oxidizing complex that includes a metal ion:Schiff base complex, andtin in the tin whisker replaces the metal to produce silvernanoparticles that are suspended in the coating. The silver ionfunctions as the oxidizer to oxidize a tin ion, and the Schiff basecomplexes the silver ion, which is replaced by the tin ion.

As used herein, the term “about” modifying the quantity of aningredient, component, or reactant of the invention employed refers tovariation in the numerical quantity that can occur, for example, throughtypical measuring and liquid handling procedures used for makingconcentrates or solutions. Furthermore, variation can occur frominadvertent error in measuring procedures, differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods, and the like. In one aspect, theterm “about” means within 10% of the reported numerical value. Inanother aspect, the term “about” means within 5% of the reportednumerical value. Yet, in another aspect, the term “about” means within10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

As used herein, the terms “Schiff base” means a compound with afunctional group having a carbon-nitrogen double bond with the nitrogenatom connected to an aryl or alkyl group. The bases described hereinhave the following formula: R₁R₂C═NR₃, wherein R₁ is a hydrogen or anorganic side chain, and R₂ and R₃ are each organic side chains.

Turning again to the Figures, FIG. 2A is a cross-sectional side view ofa metal layer 202 arranged on a substrate 201. The substrate 201 may beany surface, for example, a laminate, such as an interposer, printedcircuit board, or other device. The laminate surface may include, forexample, silicon, ceramic, glass, polymers, copper, or any combinationthereof. The substrate 201 may also a chip, such as, a board, a die, ora wafer.

The metal layer 202 is arranged on the substrate 201. Although not shownin FIG. 2A, any number or types of layers or other coatings may bepresent between the metal layer 202 and the substrate 201. For example,dielectric layers may be arranged on the substrate 201. The metal layer202 may be a tin coating, interconnect structure, solder bump, tinplated surface, or other tin-containing surface. The thickness anddimensions of the metal layer 202 shown in FIG. 2A is not drawn to scaleand is for illustrative purposes only. Further, the metal layer 202 mayonly cover a portion of the substrate 201 and does not have tosubstantially cover a surface of the substrate 201.

The metal layer 202 includes a metal. In one example, the metal is tin.The tin may be pure or substantially pure. In one embodiment, the metallayer 202 includes about 100 atomic % (at. %) tin. In other embodiments,the metal layer 202 includes tin and one or more additives to form a tinalloy. In some embodiments, the metal layer 202 may include about 97 at.% to about 100 at. % tin. In other embodiments, the metal layer 202 mayinclude about 98 at. % to about 99 at. % tin. Tin alloys may include tinand another metal, for example, silver, copper, nickel, lead, palladium,gold, or a combination thereof. In another example, the metal of themetal layer 202 is nickel. Yet, in another example, the metal of themetal layer 202 is cadmium, zinc, or indium. As mentioned above, thethickness of the metal layer 202 may generally vary and is not intendedto be limited.

FIG. 2B is a cross-sectional side view of a coating 203 arranged on themetal layer 202 of FIG. 2A according to embodiments. The coating 203 isa conformal coating layer that incorporates at least one oxidizingadditive. The oxidizing additive is impregnated within a polymericcoating material. The coating 203 includes any polymeric conformalcoating material. Non-limiting examples of polymeric materials includeurethanes, acrylics, urethane acrylics, silicones, epoxies, parylenes,or any combination thereof.

The metal complexing additive (e.g., a tin complexing additive) is addedto the polymeric material of the conformal coating before depositing onthe metal surface. The metal complexing additive thus modifies thecoating. After deposition on the metal layer 202, any metal whiskers(e.g., tin whiskers) formed from the metal layer 202 that grow into thecoating 203 are oxidized, consuming the metal whisker. The metalwhiskers thus prevented from growing from the metal surface.

The complexing additive may be any complexing agent, oxidizing agent,oxidizing compound, or oxidizing complex that reacts with and complexesmetal in the metal surface to mitigate whisker formation. In oneembodiment, the complexing additive is an oxidizing complex thatincludes an oxidizing metal ion and a Schiff base-containing compound.The oxidizing metal ion depends on the metal that is to be displaced inthe metal surface. When the metal surface includes tin and tin whiskersare the concern, the metal ion functions as the oxidizer and has astandard reduction potential (E°) that is greater than tin(Sn²⁺+2e⁻→Sn). Tin has a standard reduction potential of about −0.14volts. After reacting with the complexing additive, the tin in the tinwhiskers is in the form of a tin ion, or Sn²⁺. When the metal surfaceincludes nickel and nickel whiskers are the concern, the metal ion has aE° that is greater than nickel (Ti²⁺+2e⁻→Ti). Nickel has a standardreduction potential of about −0.25 volts. After reacting with thecomplexing additive, the nickel in the nickel whiskers is in the form ofa nickel ion, or Ni²⁺.

The Schiff base containing compound chelates or complexes the metal ion.In one embodiment, the oxidizing agent in the additive oxidizes themetal whisker according to Reaction Scheme I, after being deposited on ametal surface:metal¹+metal² ion:Schiff base→metal¹ ion:Schiff base+metal²nanoparticle;or according to Reaction Scheme II:Sn+metal ion²:(R₁R₂C═NR₃)→Sn²⁺:(R₁R₂C═NR₃)+metal²,wherein R₁ is a hydrogen or an organic side chain, and R₂ and R₃ areeach independently organic side chains, which may be the same ordifferent. The organic side chain may be a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkenyl group, a substitutedor unsubstituted alkynyl group, a substituted or unsubstituted arylgroup, a substituted or unsubstituted cycloalkyl group, or a combinationthereof. The substitutions can include any functional group, including,but not limited to, an acrylate group, an acyl halide group, an amidegroup, an amine group, a carboxylate group, a carboxylate thiol group,an epoxy group, an ester group, an ether group, a halogen, a hydroxamicacid group, a hydroxyl group, a nitrate group, a nitrile group, aphosphate group, a phosphine group, a phosphonic acid group, a silanegroup, a sulfate group, a sulfide group, a sulfite group, a thiolategroup, an azide group, an acetal group, an aldehyde group, a dienegroup, an imine group, or any combinations thereof.

When the substituted functional group in Reaction Scheme II is an iminegroup, the imine group can be another Schiff base functional group, suchthat two Schiff base complexes are present in the compound.

The metal¹ in Reaction Scheme I can be any metal present in a metalsurface, for example, tin or nickel. The metal² in Reaction Schemes Iand II can be any metal that can form a complex with the Schiff basewhen in an ionized form and be substituted for tin ions, or other metalderived from a metal surface. As mentioned above, the metal ion in thecomplex can be any metal with a standard reduction potential that isgreater than the metal, for example, greater than about −0.14 volts (thestandard reduction potential of tin). Non-limiting examples of suitablemetals for the complexing agent include silver, gold, platinum,palladium, copper, cerium, rhodium, or a combination thereof. Exemplarystandard reduction potentials are shown below in Table 1. The metals maybe present in any oxidation state, which depends on a variety offactors. In one non-limiting example, silver ions may be present as Ag⁺ions or Ag³⁺ ions.

TABLE 1 Half reaction E°/V Zn²⁺ + 2e⁻ → Zn −0.76 In³⁺ + 3e⁻ → In −0.40Cd²⁺ + 2e⁻ → Cd −0.40 Ni²⁺ + 2e⁻ → Ni −0.25 Sn²⁺ + 2e⁻ → Sn −0.14 Ag⁺ +e⁻ → Ag +0.80 Rh³⁺ + 3e⁻ → Rh +0.80 Pd²⁺ + 2e⁻ → Pd +0.99 Pt²⁺ + 2e⁻ →Pt +1.19 Au³⁺ + 3e⁻ → Au +1.50 Ce⁴⁺ + 2e⁻ → Ce³⁺ +1.61

In Reaction Schemes I and II, the metal ion²:Schiff base complex is theoxidizing complex. Upon deposition on the tin surface, metal surface,for example, tin ions in any tin whiskers extending from the tin surfacedisplaces the metal in the metal ion:Schiff base complex. Metalparticles (i.e., nanoparticles) are produced as a by-product of thereaction. Thus, the tin whiskers are consumed and mitigated.

In Reaction Schemes I and II, the molar ratios of the metal ion² toSchiff base (R₁R₂C═NR₃) are not limited to a 1:1 ratio. For example, themolar ratio of metal ion² to Schiff base (R₁R₂C═NR₃) may be 1:1, 1:2, or2:2.

In another embodiment, the oxidizing complex is a complex of a Schiffbase and silver ion (silver:Schiff base). The molar ratios of the silverion to Schiff base may be, for example, 1:1 silver to Schiff base or 1:2silver to Schiff base. The silver may be in the form of silver (I) ionsor silver (III) ions. The reaction of the silver:Schiff base complexwith the tin whiskers occurs may occur according to Reaction Scheme III:tin+silver ion:Schiff base→tin ion:Schiff base+silver nanoparticles;or according to Reaction Scheme IV:Sn+Ag^(x+):R₁R₂C═NR₃→Sn²⁺:R₁R₂C═NR₃+Ag,wherein R₁ is a hydrogen or an organic side chain, R₂ and R₃ are eachindependently organic side chains, which may be the same or different,and x is 1 or 3. The organic side chain may be a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkenyl group,a substituted or unsubstituted alkynyl group, a substituted orunsubstituted aryl group, a substituted or unsubstituted cycloalkylgroup, or a combination thereof. The substitutions can include anyfunctional group, including, but not limited to, an acrylate group, anacyl halide group, an amide group, an amine group, a carboxylate group,a carboxylate thiol group, an epoxy group, an ester group, an ethergroup, a halogen, a hydroxamic acid group, a hydroxyl group, a nitrategroup, a nitrile group, a phosphate group, a phosphine group, aphosphonic acid group, a silane group, a sulfate group, a sulfide group,a sulfite group, a thiolate group, an azide group, an acetal group, analdehyde group, a diene group, an imine group, or any combinationthereof.

In Reaction Schemes III and IV, the silver ion (Ag^(x+)):Schiff basecomplex is the oxidizing agent. Tin ions replace silver ions in thesilver (Ag^(x+)):Schiff base. Silver nanoparticles are produced as aby-product of the reaction. Thus, the tin whiskers are consumed andmitigated.

The oxidizing complex may include a symmetric Schiff base compound thatincludes at least two Schiff base functional groups. The symmetricSchiff bases chelates or complexes the silver ions in a 1:1 molar ratioor 1:2 molar ratio of silver to Schiff base compound.

In an exemplary embodiment, the oxidizing complex is a metal ion, suchas a silver ion, complexed withN,N′-bis[(4-methoxyphenyl)methylidene]ethane-1,2-diamine (MBDA)(silver:MBDA). The MBDA has the following structure (structure I):

The silver ion:MBDA complex may include additional anions, such asnitrates (NO₃). The molar ratio of silver ions to MBDA in the silverion:MBDA can be, for example, 1:1 or 1:2. For example, the complexes canbe Ag(MBDA)₂NO₃, Ag(MBDA)₂, or AgMBDA.

In another embodiment, the oxidizing complex is a metal ion, such as asilver ion, complexed withN,N′-bis[(4-methoxyphenyl)methylidene]propane-1,3-diamine (MBDB)(silver:MDBB). The MBDB has the following structure (structure II):

The silver ion:MBDB complex may include additional anions, such asnitrates (NO₃). The molar ratio of silver ions to MBDB in the silverion:MBDB can be, for example, 1:1 or 1:2. For example, the complexes canbe Ag(MBDB)₂NO₃, Ag(MBDB)₂, or AgMBDB.

Yet, in another embodiment, the oxidizing complex is a silver ion:Schiffbase complex. The Schiff base has the following structure (structureIII):

wherein R₁ and R₂ are each independently a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkenyl group, a substitutedor unsubstituted alkynyl group, a substituted or unsubstituted arylgroup, a substituted or unsubstituted cycloalkyl group, or a combinationthereof. The substitutions can include any functional group, including,but not limited to, an acrylate group, an acyl halide group, an amidegroup, an amine group, a carboxylate group, a carboxylate thiol group,an epoxy group, an ester group, an ether group, a halogen, a hydroxamicacid group, a hydroxyl group, a nitrate group, a nitrile group, aphosphate group, a phosphine group, a phosphonic acid group, a silanegroup, a sulfate group, a sulfide group, a sulfite group, a thiolategroup, an imine group, or any combination thereof.

In another embodiment, the oxidizing complex is a metal ion:Schiff basecomplex. The Schiff base has the following structure (structure IV):

wherein R₁, R₂, and R₃ are each independently a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkenyl group,a substituted or unsubstituted alkynyl group, a substituted orunsubstituted aryl group, a substituted or unsubstituted cycloalkylgroup, or a combination thereof. The substitutions can include anyfunctional group, including, but not limited to, an acrylate group, anacyl halide group, an amide group, an amine group, a carboxylate group,a carboxylate thiol group, an epoxy group, an ester group, an ethergroup, a halogen, a hydroxamic acid group, a hydroxyl group, a nitrategroup, a nitrile group, a phosphate group, a phosphine group, aphosphonic acid group, a silane group, a sulfate group, a sulfide group,a sulfite group, a thiolate group, an imine group, or any combinationthereof.

In one embodiment, the oxidizing complex is a metal ion:Schiff basecomplex, and the Schiff base has the following structure (structure V):

wherein R is a substituted or unsubstituted alkyl group, a substitutedor unsubstituted alkenyl group, a substituted or unsubstituted alkynylgroup, a substituted or unsubstituted aryl group, a substituted orunsubstituted cycloalkyl group, or a combination thereof. Thesubstitutions can include any functional group, including, but notlimited to, an acrylate group, an acyl halide group, an amide group, anamine group, a carboxylate group, a carboxylate thiol group, an epoxygroup, an ester group, an ether group, a halogen, a hydroxamic acidgroup, a hydroxyl group, a nitrate group, a nitrile group, a phosphategroup, a phosphine group, a phosphonic acid group, a silane group, asulfate group, a sulfide group, a sulfite group, a thiolate group, animine group, or any combination thereof. In one example, the Schiff basehas the following structure (structure VI):

In an embodiment, the oxidizing complex is a metal ion:Schiff basecomplex, and the Schiff base has the following structure (structureVII):

wherein R is a substituted or unsubstituted alkyl group, a substitutedor unsubstituted alkenyl group, a substituted or unsubstituted alkynylgroup, a substituted or unsubstituted aryl group, a substituted orunsubstituted cycloalkyl group, or a combination thereof. Thesubstitutions can include any functional group, including, but notlimited to, an acrylate group, an acyl halide group, an amide group, anamine group, a carboxylate group, a carboxylate thiol group, an epoxygroup, an ester group, an ether group, a halogen, a hydroxamic acidgroup, a hydroxyl group, a nitrate group, a nitrile group, a phosphategroup, a phosphine group, a phosphonic acid group, a silane group, asulfate group, a sulfide group, a sulfite group, a thiolate group, animine group, or any combination thereof. In one example, the Schiff baseis a salen having the following structure (structure VIII):

Other non-limiting examples of Schiff bases include salicylaldoximes(salicylaldehyde oximes), salens (N,N′-Ethylenebis(salicylimine)), andsalen-type ligands.

In another embodiment, the oxidizing complex is a metal ion:Schiff basecomplex, and the Schiff base has the following structure (structure IX):

wherein R is a substituted or unsubstituted alkyl group, a substitutedor unsubstituted alkenyl group, a substituted or unsubstituted alkynylgroup, a substituted or unsubstituted aryl group, a substituted orunsubstituted cycloalkyl group, or a combination thereof. Thesubstitutions can include any functional group, including, but notlimited to, an acrylate group, an acyl halide group, an amide group, anamine group, a carboxylate group, a carboxylate thiol group, an epoxygroup, an ester group, an ether group, a halogen, a hydroxamic acidgroup, a hydroxyl group, a nitrate group, a nitrile group, a phosphategroup, a phosphine group, a phosphonic acid group, a silane group, asulfate group, a sulfide group, a sulfite group, a thiolate group, animine group, or any combination thereof. In one example, the Schiff baseis derived from a salen and has the following structure (structure X):

In another exemplary embodiment, the oxidizing complex is a metalion:Schiff base complex having the following structure (structure XI):

wherein M is a metal ion selected from silver, gold, platinum,palladium, copper, cerium, or rhodium. The metal ion may be in anyoxidation state.

The above-described metal ion:Schiff base complexes, and silverion:Schiff base complexes may be synthesized using known methods. TheSchiff bases compounds are initially synthesized using known methods.Then the metal complexes may be formed by adding a metal salt solutionto the Schiff base compound. The metal salt solution can be, forexample, silver nitrate, when silver is used as the metal ion. Becausemetal salt solutions are used to form the complexes, additional anionsmay be included in the resulting complexes after reacting with the metalwhiskers. Examples of anions that may also be present in the complexesinclude acetates, carbonates, chlorides, citrates, cyanides, fluorides,nitrates, nitrites, oxides, phosphates, sulfates, or any combinationthereof. In the coating described above with the metal ion:Schiff basecomplex additives, the Schiff bases are in a deprotonated (basic) form.

The complexing additive in the coating 203 is not limited to the abovemetal ion:Schiff base complexes and can be any complexing additive thatcan be suitably incorporated into the coating, provided that theadditive reacts with tin to consume the tin in the whiskers. Thecomplexing additive may be a compound or molecule that has a standardreduction potential that is greater than the metal in the metal surface,for example, tin. The complexing agent may also be an oxidizing complex.The reaction may occur according to Reaction Scheme V:metal+complexing agent→metal ion:complexing agent.

In Reaction Scheme V, the complexing agent reacts with the metal (e.g.,tin) in the metal whiskers to form a complex (metal ion:complexingagent), which consumes the metal and eliminates the whiskers beneath andwithin the coating. Non-limiting examples of suitable complexing agentsinclude molecules and compounds that include porphyrins, substitutedporphyrins, corroles, substituted corroles, carbaporphyrins, substitutedcarbaporphyrins, aminopolycarboxylic acids (i.e.,ethylenediametetraacetic acid (EDTA)), phthalocyanines, substitutedphthalocyanines, or other like molecules and compounds.

The thickness of the coating 203 may generally vary and is not intendedto be limited. One or more layers of the coating 203 may be combined toform a thicker overall coating layer. The thickness of the coating 203depends on the type of tin layer 202, device, and contents of coatingitself. In some embodiments, the coating 203 has a thickness in a rangefrom about 0.1 to about 20 millimeters (mm). In other embodiments, thecoating 203 has a thickness in a range from about 1 to about 10 mm.

The coating 203 may be applied to the metal layer 202 using any suitabledeposition method known to those skilled in the art, which depends onthe type of tin surface, device, and type of coating 203. The coating203 may be deposited by, for example, spraying or dipping. The coating203 may be deposited under suitable conditions (i.e., temperature andpressure) which depend on the deposition method.

The above-described coatings may be used on any devices or applicationshaving tin-containing surfaces that may form tin whiskers. Such devicesinclude, but are not limited to, circuit boards, electrical componentleads, electronic packaging, or other like devices.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

While the preferred embodiments to the invention have been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. A coating for mitigating metal whiskers on ametal surface, comprising: a polymeric coating material arranged on themetal surface, the metal surface being a surface of an electroniccomponent or device; and a metal ion complexing agent impregnated withinthe polymeric coating material, the metal ion complexing agentcomprising two Schiff base functional groups that chelate a metal ion,and having a standard reduction potential (E°) that is greater than ametal in the metal surface, such that the metal in the metal surface canbe oxidized to displace the metal ion in the metal ion complexing agent;wherein the metal ion complexing agent has the following structure:

wherein R₁ and R₂ are each independently a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkenyl group, a substitutedor unsubstituted alkynyl group, a substituted or unsubstituted arylgroup, a substituted or unsubstituted cycloalkyl group, or a combinationthereof; and a substitution on a substituted alkyl group, alkenyl group,alkynyl group, aryl group, or cycloalkyl group is an acrylate group, anacyl halide group, an amide group, an amine group, a carboxylate group,a carboxylate thiol group, an epoxy group, an ester group, an ethergroup, a halogen, a hydroxamic acid group, a hydroxyl group, a nitrategroup, a nitrile group, a phosphate group, a phosphine group, aphosphonic acid group, a silane group, a sulfate group, a sulfide group,a sulfite group, a thiolate group, an azide group, an acetal group, analdehyde group, a diene group, an imine group, or any combinationthereof.
 2. The coating of claim 1, wherein tin in a tin whisker candisplace the metal ion.
 3. The coating of claim 2, wherein the metal ionis a silver ion.
 4. The coating of claim 2, wherein the metal ion is agold ion.
 5. The coating of claim 2, wherein the metal ion is a platinumion.
 6. The coating of claim 2, wherein the metal ion is a palladiumion.
 7. The coating of claim 2, wherein the metal ion is a copper ion.8. The coating of claim 2, wherein the metal ion is a cerium ion.
 9. Thecoating of claim 2, wherein the metal ion is a rhodium ion.
 10. Thecoating of claim 1, wherein the metal of the metal surface is tin, andthe E° of the metal ion complexing agent is greater than −0.14 volts.11. The coating of claim 1, wherein the metal of the metal surface isnickel, and the E° of the metal ion complexing agent is greater than−0.25 volts.
 12. The coating of claim 1, wherein the coating is disposedon a tin surface comprising about 97 to about 100 atomic % (at. %) tin.13. The coating of claim 1, wherein the metal ion complexing agentchelates tin.
 14. The coating of claim 1, wherein the polymeric coatinghas a thickness in a range from about 0.1 to about 20 millimeters (mm).15. The coating of claim 1, wherein the metal surface comprises tin. 16.The coating of claim 1, wherein the metal surface comprises pure orsubstantially pure tin.
 17. A coating for mitigating metal whiskers on ametal surface, comprising: a polymeric coating material arranged on themetal surface, the metal surface being a surface of an electroniccomponent or device; and a metal ion complexing agent impregnated withinthe polymeric coating material, the metal ion complexing agentcomprising two Schiff base functional groups that chelate a metal ion,and having a standard reduction potential (E°) that is greater than ametal in the metal surface, such that the metal in the metal surface canbe oxidized to displace the metal ion in the metal ion complexing agent;wherein the metal ion complexing agent has the following structure: